BlackBerry Maps resolution in MapView

I'm having problems with the resolution of Blackberry maps in MapView.

To test it wasn't me, I modified the mapview cascades example to show my home address. I can zoom in to the neighbourhood with pinch gestures, and I can see the street but not its name. I zoom in slightly more and I get a grey screen until I zoom back out.

Is there some limit on resolution of BB10 maps on the Dev Alpha currently, or is it just a bug in Beta 4's MapView?

Btw, the map rendering is pretty awful too. New tiles seem to appear at higher resolution than required and then slowly repaint correctly. It looks terrible...